Andrew Richards & Ryan Swenson

Endochondral Ossification-”within cartilage”

• Start with Hyaline cartilage model in similar shape as the bone• Primary ossification center expands from the center

Vasculature, bone marrow cells, osteoblast, and osteoclasts spread throughout diaphysis

• Osteoblasts deposit matrix, results in spongy trabeculae, then medullary cavity

• Blood vessels penetrate epiphysis to form secondary ossification center• Cartilage remains between two ossification centers-epiphyseal plate• Most bones form in this way

Intramembranous Ossification-”within membrane”• Mesenchymal cells differentiate into osteoblasts• Form ossification center, and secrete bone matrix

• Osteoblasts encased in matrix become osteocytes• Network of trabeculae forms around blood vessels• Trabeculae thicken to form plates of compact bone• Bones of skull and clavicle form in this way

Osteoclast-resorb old bone• Dissolve and digest, form lacunae and Haversian

canals Osteoblast-synthesize new bone matrix

• Encase themselves in matrix Osteocyte-terminal osteoblasts

• Lie within mineralized bone, no longer produce matrix

• Function as support structure and metabolism

Longitudinal growth• Occurs at the Epiphyseal plate• Childhood and adolescence

Radial Growth Occurs during modeling inresponse to environmental Factors (Adapt)

Process of resorbing old bone and forming new Occurs throughout lifespan

• Body usually in “bone balance”• In older age negative balance, bones become

brittle Resorption, Reversal, and Formation

Resorption• Osteoclasts are activated to resorb bone

through many chemical reactions• Result in lacunae in trabecular bone and

Haversian canals in cortical bone• Resorption cycles last approximately 2-4

weeks

Reversal• Process transitions to bone formation• Resorpton cavities (lacuna and canals)

contain a variety of mononuclear cells Ex. monocytes, and preosteoblasts

Formation• Osteoblasts synthesize new collagenous

matrix• Encase themselves in their matrix • Become osteocytes

Percentage undergo apoptosis and become bone lining cells